Heat treated ceramic substrate having ceramic coating

ABSTRACT

A heat treated ceramic article includes a ceramic substrate and a ceramic coating on the ceramic substrate. The ceramic coating is a non-sintered ceramic coating that has a different composition than the ceramic substrate. The heat treated ceramic article further includes a transition layer between the ceramic substrate and the ceramic coating, the transition layer comprising first elements from the ceramic coating that have reacted with second elements from the ceramic substrate, wherein the transition layer has a thickness of about 0.1 microns to about 5 microns.

RELATED APPLICATIONS

This patent application is a divisional application of U.S. patentapplication Ser. No. 14/938,624, filed Nov. 11, 2015, which is adivisional application of U.S. patent application Ser. No. 13/745,589,filed Jan. 18, 2013, which claims the benefit under 35 U.S.C. § 119(e)of U.S. Provisional Application No. 61/602,020, filed Feb. 22, 2012 andof U.S. Provisional Application No. 61/619,854, filed Apr. 3, 2012. Thispatent application herein incorporates parent applications Ser. Nos.14/938,624 and 13/745,589 by reference.

TECHNICAL FIELD

Embodiments of the present invention relate, in general, to a heattreatment process used to heat treat coated ceramic articles.

BACKGROUND

In the semiconductor industry, devices are fabricated by a number ofmanufacturing processes producing structures of an ever-decreasing size.Some manufacturing processes such as plasma etch and plasma cleanprocesses expose a substrate to a high-speed stream of plasma to etch orclean the substrate. The plasma may be highly corrosive, and may corrodeprocessing chambers and other surfaces that are exposed to the plasma.This corrosion may generate particles, which frequently contaminate thesubstrate that is being processed, contributing to device defects.

As device geometries shrink, susceptibility to defects increases, andparticle contaminant requirements become more stringent. Accordingly, asdevice geometries shrink, allowable levels of particle contamination maybe reduced. To minimize particle contamination introduced by plasma etchand/or plasma clean processes, chamber materials have been developedthat are resistant to plasmas. Examples of such plasma resistantmaterials include ceramics composed of Al₂O₃, AlN, SiC, Y₂O₃, quartz,and ZrO2. However, the plasma resistance properties of these ceramicmaterials may be insufficient for some applications. For example, plasmaresistant ceramic lids and/or nozzles that are manufactured usingtraditional ceramic manufacturing processes may produce unacceptablelevels of particle contamination when used in plasma etch processes ofsemiconductor devices with critical dimensions of 45 nm or 32 nm.Additionally, when such plasma resistant ceramics are used as ceramiccoatings, these coatings may cause elevated levels of particlecontamination and may fail due to delamination.

SUMMARY

In one embodiment, a ceramic article includes a ceramic substrate and aceramic coating on the ceramic substrate. The ceramic article isproduced by a process that includes performing a thermal sprayingprocess to form the ceramic coating on the ceramic substrate, theceramic coating having an initial porosity and an initial amount ofcracking. The process additionally includes heating the ceramic articleto a temperature range between about 1000° C. and about 1800° C. at aramping rate of about 0.1° C. per minute to about 20° C. per minute. Theprocess additionally includes performing heat treatment of the ceramicarticle at one or more temperatures within the temperature range for aduration of up to about 24 hours to reduce a porosity of the ceramiccoating to below the initial porosity and to reduce an amount ofcracking of the ceramic coating to below the initial amount of cracking,wherein the ceramic article is heat treated at below a sinteringtemperature for the ceramic coating to prevent sintering of the ceramiccoating. The process additionally includes cooling the ceramic articleat the ramping rate after the heat treatment, wherein after the heattreatment the ceramic coating is not sintered, has a reduced amount ofcracking that is below the initial amount of cracking, and has a reducedporosity that is below the initial porosity.

In one embodiment, a ceramic article includes a ceramic substrate and aceramic coating on the ceramic substrate, wherein the ceramic coating isa non-sintered ceramic coating that has a different composition than theceramic substrate. The ceramic article additionally includes atransition layer between the ceramic substrate and the ceramic coating,the transition layer including first elements from the ceramic coatingthat have reacted with second elements from the ceramic substrate. Thetransition layer has a thickness of about 0.1 microns to about 5microns.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that differentreferences to “an” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone.

FIG. 1A illustrates an exemplary architecture of a manufacturing system,in accordance with one embodiment of the present invention;

FIG. 1B illustrates a process for heat treating a ceramic article, inaccordance with one embodiment of the present invention;

FIG. 2A shows micrographs of a ceramic coating's surface before theceramic coating is processed using a heat treatment, and after theceramic coating has been processed using the heat treatment, inaccordance with embodiments of the present invention;

FIG. 2B shows additional micrographs of a ceramic coating's surface at a4,000-fold magnification before the ceramic coating is processed using aheat treatment, and after the ceramic coating has been processed usingheat treatments at various temperatures and treatment durations, inaccordance with embodiments of the present invention;

FIG. 2C shows additional micrographs of a ceramic coating's surface at a20,000-fold magnification before the ceramic coating is processed, andafter the ceramic coating has been processed using heat treatments ofvarious temperatures and treatment durations, in accordance withembodiments of the present invention;

FIG. 2D shows additional micrographs of a ceramic coating's surface at a10,000-fold magnification before the ceramic coating is processed, andafter the ceramic coating has been processed, in accordance withembodiments of the present invention;

FIG. 3A illustrates micrographs showing a cross sectional side view of aceramic article before and after heat treatment, in accordance with oneembodiment of the present invention;

FIG. 3B illustrates micrographs showing cross sectional side views of aceramic article at a 4,000-fold magnification before and after heattreatment at various temperatures and treatment durations, in accordancewith embodiments of the present invention;

FIG. 3C illustrates micrographs showing cross sectional side views of aceramic article at a 20,000-fold magnification before and after heattreatment, in accordance with embodiments of the present invention;

FIG. 3D illustrates a phase composition comparison of an HPM ceramiccomposite coating before and after heat treatment, in accordance withone embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the invention are directed to a process for heat treatinga ceramic article, and to a ceramic article processed using the heattreatment. In one embodiment, a ceramic article including a ceramicsubstrate and a ceramic coating having an initial porosity, an initialbond strength to the ceramic substrate and an initial amount of crackingis provided. The ceramic substrate may be a sintered ceramic, and theceramic coating may be a plasma sprayed ceramic. The ceramic article maybe, for example, a ceramic lid, nozzle or process kit for a plasmaetcher. The ceramic article is heated to a temperature range betweenabout 1000° C. and about 1800° C. at a ramping rate of about 0.1° C. perminute to about 20° C. per minute. The ceramic article is heat treatedat one or more temperatures within the temperature range for a durationof up to about 24 hours. The ceramic article is then cooled at theramping rate. After the heat treatment, the ceramic coating has reducedsurface defects, a reduced coating porosity and a reduced amount ofcracking. The ceramic coating may also have a reduced surface roughness,and may additionally have a greater resistance to plasma. Additionally,after the heat treatment, the ceramic coating may have a strongerinterface to the ceramic substrate, which may provide a greater adhesionstrength to the ceramic substrate. The stronger interface may be due tothe formation of a transition layer between the ceramic substrate andthe ceramic coating.

In one embodiment, a furnace performs a heat treatment process on aceramic article including a ceramic substrate and a ceramic coatinghaving an initial porosity and an initial amount of cracking. Thefurnace heats the ceramic article at a ramping rate of about 0.1° C. perminute to about 20° C. per minute until the ceramic article reaches aspecified temperature or temperature range. The specified temperaturerange may vary from about 1000° C. to about 1800° C., and the specifiedtemperature may be a temperature within the specified temperature range.The furnace heat treats the ceramic article at the specified temperatureand/or other specified temperatures within the temperature range for aduration of up to about 24 hours. The furnace then cools the ceramicarticle at the ramping rate. After the heat treatment, the ceramicarticle has a reduced surface porosity and a reduced amount of cracking.

Embodiments of the invention increase the strength of a bond between theceramic coating and the ceramic substrate that it coats through aformation of transition layer. Embodiments of the invention also reducethe surface defects, reduce the porosity and reduce the amount ofcracking of a ceramic coating on a processed ceramic article.Embodiments may also reduce the surface roughness of processed ceramiccoatings, and minimize surface particles on the ceramic coatings. Suchheat treated ceramic coatings have a reduced number of high energy bonds(broken bonds), and may produce a significantly lower amount of particlecontamination when used in semiconductor processes that apply plasmas(e.g., plasma etch and plasma clean processes). Additionally, thereduced porosity and reduced cracking of the heat treated ceramiccoating reduces an amount of process gas that penetrates the ceramiccoating to react with an underlying substrate. Additionally, theformation of a transition layer (also referred to herein as aninterfacial transition layer) between the ceramic coating and ceramicsubstrate prohibits the reaction of process chemistry that penetratesthe coating with an underlying substrate. This may minimize theoccurrence of delamination. The transition layer may increase adhesionstrength of the ceramic coating, and may minimize peeling. For example,ceramic coated lids and nozzles for etcher machines may be heat treatedto minimize particle contamination and/or peeling introduced duringplasma etch processes. Thus, semiconductors manufactured using the heattreated ceramic articles described herein may have a lower defect countand may result in reduced scrap rates.

The term “heat treating” is used herein to mean applying an elevatedtemperature to a ceramic article, such as by a furnace. When the term“about” is used herein, this is intended to mean that the nominal valuepresented is precise within ±10%.

Some embodiments are described herein with reference to using a furnaceto perform a heat treatment. However, it should be understood that otherheat treatment techniques may also be used to perform the described heattreatment. Some examples of additional heat treatment techniques thatmay be used include a laser surface treatment (also referred to as laserheat treatment), an electron beam (e-beam) surface treatment (alsoreferred to as e-beam heat treatment), a flame surface treatment (alsoreferred to as a flame heat treatment), and a high temperature plasmatreatment.

Note also that some embodiments are described herein with reference toceramic coated lids and ceramic coated nozzles used in plasma etchersfor semiconductor manufacturing. However, it should be understood thatsuch plasma etchers may also be used to manufacturemicro-electro-mechanical systems (MEMS)) devices. Additionally, the heattreated ceramic articles described herein may be other structures thatare exposed to plasma. For example, the ceramic articles may be ceramiccoated rings, walls, bases, gas distribution plates, shower heads,substrate holding frames, etc. of a plasma etcher, a plasma cleaner, aplasma propulsion system, and so forth.

Moreover, embodiments are described herein with reference to ceramicarticles that cause reduced particle contamination when used in aprocess chamber for plasma rich processes. However, it should beunderstood that the ceramic articles discussed herein may also providereduced particle contamination when used in process chambers for otherprocesses such as non-plasma etchers, non-plasma cleaners, chemicalvapor deposition (CVD) chambers physical vapor deposition (PVD)chambers, plasma enhanced chemical vapor deposition (PECVD) chambers,plasma enhanced physical vapor deposition (PEPVD) chambers, plasmaenhanced atomic layer deposition (PEALD) chambers, and so forth.

FIG. 1A illustrates an exemplary architecture of a manufacturing system,in accordance with one embodiment of the present invention. Themanufacturing system 100 may be a ceramics manufacturing system. In oneembodiment, the manufacturing system 100 includes a furnace 105 (e.g., aceramic furnace such as a kiln), an equipment automation layer 115 and acomputing device 120. In alternative embodiments, the manufacturingsystem 100 may include more or fewer components. For example, themanufacturing system 100 may include only the furnace 105, which may bea manual off-line machine.

Furnace 105 is a machine designed to heat articles such as ceramicarticles. Furnace 105 includes a thermally insulated chamber, or oven,capable of applying a controlled temperature on articles (e.g., ceramicarticles) inserted therein. In one embodiment, the chamber ishermitically sealed. Furnace 105 may include a pump to pump air out ofthe chamber, and thus to create a vacuum within the chamber. Furnace 105may additionally or alternatively include a gas inlet to pump gasses(e.g., inert gasses such as Ar or N₂) into the chamber.

Furnace 105 may be a manual furnace having a temperature controller thatis manually set by a technician during processing of ceramic articles.Furnace 105 may also be an off-line machine that can be programmed witha process recipe. The process recipe may control ramp up rates, rampdown rates, process times, temperatures, pressure, gas flows, and so on.Alternatively, furnace 105 may be an on-line automated furnace that canreceive process recipes from computing devices 120 such as personalcomputers, server machines, etc. via an equipment automation layer 115.The equipment automation layer 115 may interconnect the furnace 105 withcomputing devices 120, with other manufacturing machines, with metrologytools and/or other devices.

The equipment automation layer 115 may include a network (e.g., alocation area network (LAN)), routers, gateways, servers, data stores,and so on. Furnace 105 may connect to the equipment automation layer 115via a SEMI Equipment Communications Standard/Generic Equipment Model(SECS/GEM) interface, via an Ethernet interface, and/or via otherinterfaces. In one embodiment, the equipment automation layer 115enables process data (e.g., data collected by furnace 105 during aprocess run) to be stored in a data store (not shown). In an alternativeembodiment, the computing device 120 connects directly to the furnace105.

In one embodiment, furnace 105 includes a programmable controller thatcan load, store and execute process recipes. The programmable controllermay control temperature settings, gas and/or vacuum settings, timesettings, etc. of heat treat processes. The programmable controller maycontrol a chamber heat up, may enable temperature to be ramped down aswell as ramped up, may enable multi-step heat treating to be input as asingle process, and so forth. The programmable controller may include amain memory (e.g., read-only memory (ROM), flash memory, dynamic randomaccess memory (DRAM), static random access memory (SRAM), etc.), and/ora secondary memory (e.g., a data storage device such as a disk drive).The main memory and/or secondary memory may store instructions forperforming heat treatment processes described herein.

The programmable controller may also include a processing device coupledto the main memory and/or secondary memory (e.g., via a bus) to executethe instructions. The processing device may be a general-purposeprocessing device such as a microprocessor, central processing unit, orthe like. The processing device may also be a special-purpose processingdevice such as an application specific integrated circuit (ASIC), afield programmable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. In one embodiment, programmablecontroller is a programmable logic controller (PLC).

In one embodiment, furnace 105 is programmed to execute a recipe thatwill cause the furnace 105 to heat treat a ceramic article using a heattreatment process described with reference to FIG. 1B.

FIG. 1B is a flow chart showing a process 150 for heat treating aceramic article, in accordance with one embodiment of the presentinvention. At block 155 of process 150, a ceramic article is provided(e.g., to a furnace or kiln). In one embodiment, the ceramic article isautomatically loaded into a furnace by a loader. The ceramic articleincludes a ceramic substrate that has been coated on at least onesurface with a ceramic coating. In one embodiment, the ceramic articleis a ceramic lid, a ceramic nozzle, or another process chamber elementfor a plasma etcher or plasma cleaner. The ceramic article may have ayttria dominant ceramic coating. Yttria dominant ceramics may be useddue to the superior plasma resistance properties of yttria oxides. Theceramic article may also have a ceramic substrate that has goodmechanical properties such as a high flexural strength and resistance tocracking due to high temperatures and/or thermal stress.

The ceramic substrate may have been machined prior to being coated withthe ceramic coating. Additionally, the ceramic coating may have beenmachined after having coated the ceramic substrate. Examples ofmachining include surface grinding, polishing, drilling, abrading,cutting, bead blasting, or otherwise processing with machine tools. Inone embodiment, after the ceramic coating is formed over the ceramicsubstrate, the ceramic coating is polished. This may cause a largeamount of particles, which may be trapped in cracks, pores and othersurface defects of the ceramic coating.

The ceramic substrate may be formed from a bulk ceramic such as Y₂O₃,Y₄Al₂O₉, Al₂O₃, Y₃Al₅O₁₂ (YAG), Quartz, SiC, Si₃N₄, AN, ZrO2, and so on.For example, the ceramic substrate may be a bulk sintered form of any ofthe ceramics described below with reference to the ceramic coating. Thesubstrate may also be a ceramic composite such as an Al₂O₃-YAG ceramiccomposite or a SiC—Si₃N₄ ceramic composite. The ceramic substrate mayalso be a ceramic composite that includes a yttrium oxide (also known asyttria and Y₂O₃) containing solid solution. For example, the ceramicsubstrate may be a high performance material (HPM) that is composed of acompound Y₄Al₂O₉ (YAM) and a solid solution Y₂-xZr_(x)O₃ (Y₂O₃—ZrO₂solid solution). Note that pure yttrium oxide as well as yttrium oxidecontaining solid solutions may be doped with one or more of ZrO₂, Al₂O₃,SiO₂, B₂O₃, Er₂O₃, Nd₂O₃, Nb₂O₅, CeO₂, Sm₂O₃, Yb₂O₃, or other oxides.

Similar to the ceramic substrate, the ceramic coating may be formed ofY₂O₃ (yttria), Y₄Al₂O₉ (YAM), Al₂O₃ (alumina), Y₃Al₅O₁₂ (YAG), Quartz,YAlO₃ (YAP), SiC (silicon carbide), Si₃N₄ (silicon nitride), MN(aluminum nitride), ZrO₂ (zirconia), AlON (aluminum oxynitride), TiO₂(titania), TiC (titanium carbide), ZrC (zirconium carbide), TiN(titanium nitride), TiCN (titanium carbon nitride), Y₂O₃ stabilized ZrO₂(YSZ), and so on. Also similar to the ceramic substrate, the ceramiccoating may be pure yttrium oxide or a yttrium oxide containing solidsolution that may be doped with one or more of ZrO₂, Al₂O₃, SiO₂, B₂O₃,Er₂O₃, Nd₂O₃, Nb₂O₅, CeO₂, Sm₂O₃, Yb₂O₃, or other oxides. In oneembodiment, the ceramic coating is the HPM composite. However, theceramic coating is formed by spraying or growing the ceramic coating onthe ceramic substrate, and the ceramic substrate may be formed by asintering process.

In one embodiment, the ceramic coating is a yttrium oxide containingceramic that has been deposited on the ceramic substrate using a thermalspraying technique or plasma sprayed technique. Thermal sprayingtechniques may melt materials (e.g., ceramic powders) and spray themelted materials onto the ceramic substrate. The thermally sprayedceramic coating may have a thickness about 20 micrometers to aboutseveral millimeters.

In one embodiment, the ceramic coating is plasma sprayed onto theceramic substrate. Alternatively, other thermal spraying techniques suchas detonation spraying, wire arc spraying, high velocity oxygen fuel(HVOF) spraying, flame spraying, warm spraying and cold spraying may beused. Additionally, other coating processes such as aerosol deposition,electroplating, physical vapor deposition (PVD), ion assisted deposition(IAD) and chemical vapor deposition (CVD) may be used to form theceramic coating. Notably, the ceramic coating process may produce aceramic coating having small voids such as pores, cracks and regions ofincomplete bonding. The ceramic coating may have structural propertiesthat are significantly different from those of bulk ceramic materials(e.g., such as the ceramic substrate).

In one embodiment, the ceramic coating is produced from Y₂O₃ powder.Alternatively, the ceramic coating may be a HPM ceramic compositeproduced from a mixture of a Y₂O₃ powder, ZrO₂ powder and Al₂O₃ powder.In one embodiment, the HPM ceramic composite contains 77% Y₂O₃, 15% ZrO₂and 8% Al₂O₃. In another embodiment, the HPM ceramic composite contains63% Y₂O₃, 23% ZrO₂ and 14% Al₂O₃. In still another embodiment, the HPMceramic composite contains 55% Y₂O₃, 20% ZrO₂ and 25% Al₂O₃. Relativepercentages may be in molar ratios. For example, the HPM ceramic maycontain 77 mol % Y₂O₃, 15 mol % ZrO₂ and 8 mol % Al₂O₃. Otherdistributions of these ceramic powders may also be used for the HPMmaterial.

The ceramic coating may initially have a weak adhesion strength (e.g.,around 3 mega pascals (MPa)). This may cause the ceramic coating todelaminate or peel off of the ceramic substrate after time (e.g., as aresult of using the ceramic article in plasma rich processes).Additionally, the ceramic coating may have an initial porosity and aninitial amount of cracking. These pores and cracks may enable processgasses and cleaning chemistries to penetrate the ceramic coating andreact with the underlying ceramic substrate during processing. Suchreactions may generate gasses, moisture or a different material underthe ceramic coating, which may introduce blisters under the ceramiccoating. These blisters may further cause the ceramic coating toseparate from the ceramic substrate. Such separation may cause anelevated amount of particle contamination on processed material (e.g.,processed wafers). Additionally, the blisters, cracks and pores (as wellas other surface defects) may themselves cause particle contamination toprocessed substrates even in the absence of peeling.

In one example, pores, cracks, voids and other surface defects in theceramic coating may include broken (or open) bonds that are high energylocations. These surface defects may trap particles. For example, theparticles may form weak broken bonds with the ceramic article at thesurface defect. During a plasma treatment, the plasma may break theseweak broken bonds, and remove some of the particles from the ceramiccoating. The ceramic particles may then be deposited on a processedsubstrate. Moreover, the plasma may break bonds of the ceramic articleat the defect sites, at the pores, at the cracking, etc., which mayerode the ceramic coating and cause additional particles to be created.

At block 160, the ceramic article is heated at a ramping rate of about0.1° C. to about 20° C. per minute. Ceramic articles may be fragile, andmay crack when exposed to extreme changes in temperature. Accordingly, aramping rate that is slow enough to prevent the ceramic article fromcracking is used. It is expected that for some ceramics a ramping rateof more than 20° C. per minute may be possible. Accordingly, in someembodiments, ramping rates beyond 20° C. per minute that do not causecracking may be used.

The temperature changes that cause a ceramic article to crack may dependon the composition of the ceramic article. For example, Al₂O₃ may beheated at a rate of 10° C. per minute or more without cracking. However,Y₂O₃ may crack if heated at a ramping rate that is faster than about 5°C. per minute. In one embodiment, a ramping rate of about 0.1-5° C. perminute is used for ceramic coatings of Y₂O₃ and of the HPM ceramiccomposite. In a further embodiment, a ramping rate of about 5° C. perminute is used for ceramic coatings made up of Y₂O₃ and of the HPMceramic composite. Typically, the ceramic article will start at or nearambient temperature, and will slowly be heated at the ramping rate to apredetermined temperature.

The ceramic article is heated until it reaches a specified temperatureor temperature range. The specified temperature may range from about1000° C. to about 1800° C. The specific temperature used may depend onthe composition of the ceramic article or a specified target thicknessfor a transition layer. In one embodiment, a temperature of 1400-1500°C. is used for a ceramic article having an alumina substrate and an HPMceramic coating or a yttria (Y₂O₃) ceramic coating.

At block 165, the ceramic article is heat treated at the specifiedtemperature or at one or more temperatures within the temperature rangefor a duration of up to 24 hours. The specific duration used may dependon a composition of the ceramic article, as well as desired performanceproperties of the ceramic article. For example, the specific durationmay depend on a target thickness for the transition layer.

As discussed above, the ceramic coating may have a high number ofsurface defects and particles that are trapped by these surface defects.The heat treatment may reduce or eliminate these defects and/orparticles. Specifically, the heat treatment may cause the particles tomelt and/or may cause a portion of the ceramic coating to melt at thesurface defect regions. The melted particles may flow together with theceramic coating at the surface defect regions. The melted particles maythen redeposit onto the ceramic coating and form unbroken bonds with theceramic coating at these surface defect regions. The resultant unbrokenbonds are much stronger than the broken bonds that previously bound theparticles to the ceramic coating. Thus, the particles become much lesssusceptible to being removed from the ceramic coating during a plasmaetch process, and the defect regions become less susceptible to erosion.

Additionally, the ceramic coating typically has a relatively highporosity and a relatively high amount of cracking. The heat treatmentmay cause the pores and the cracks to shrink and/or be removed. Thepores and cracks may shrink or be eliminated based on the same meltingand re-depositing of the ceramic coating discussed above. For example,the ceramic coating at a pore or crack may melt and then redeposit,filling and/or healing the pore or crack.

In one embodiment, the ceramic coating and the ceramic substrate reactduring the heat treatment process to form a transition layer. Thetransition layer may be formed if the ceramic coating and the ceramicsubstrate are composed of materials that will react when exposed toheat. For example, if the ceramic substrate is Al₂O₃, and the ceramiccoating is the HPM ceramic composite, then the ceramic coating andceramic substrate will react during the heat treatment to form a YAGtransition layer. In another example, if the ceramic substrate is Al₂O₃,and the ceramic coating is Y₂O₃, then the ceramic coating and ceramicsubstrate may react during the heat treatment to form a YAG transitionlayer. Other combinations of ceramic coating materials and ceramicsubstrate materials will form other transition layers.

Notably, the transition layer may be a non-reactive and non-porouslayer. Accordingly, during subsequent processing using a heat treatedceramic article, process gases may penetrate the ceramic coating, butmay not penetrate the transition layer. Thus, the transition layer mayprevent the process gasses from reacting with the ceramic substrate.This may minimize or prevent blistering, and may improve peelingperformance and adhesion strength (bond strength)for the ceramiccoating.

Though the transition layer has numerous beneficial effects, thetransition layer may become problematic if the transition layer becomestoo thick. Some transition layers will have different coefficients ofexpansion than the ceramic coating and/or ceramic substrate. Thus, ifthe transition layer is thicker than a threshold thickness (e.g., around5 microns), then the transition layer may introduce cracking in theceramic coating during subsequent processing. For example, the HPMceramic composite and alumina have approximately equivalent coefficientsof expansion, but a transition layer of YAG has a coefficient ofexpansion that is different from the HPM ceramic composite and alumina.Thus, expansion and contraction of the YAG transition layer may causethe ceramic coating to crack if the YAG transition layer is thicker thanaround 5 microns (μm).

The transition layer grows at a rate that is dependent upon temperatureand time. As temperature and heat treatment duration increase, thethickness of the transition layer also increases. Accordingly, thetemperature (or temperatures) and the duration used to heat treat theceramic article should be chosen to form a transition layer that is notthicker than around 5 microns. In one embodiment, the temperature andduration are selected to cause a transition layer of about 0.1 micronsto about 5 microns to be formed. In one embodiment, the transition layerhas a minimum thickness that is sufficient to prevent gas from reactingwith the ceramic substrate during processing (e.g., around 0.1 microns).In one embodiment, the transition layer has a target thickness of 1-2microns.

The heat treatment also causes the grain size of the ceramic coating toincrease. As the temperature and heat treatment duration increase, thegrain size of the ceramic coating also increases. The increase of grainsize leads to fewer grain boundaries. Grain boundaries are more easilyeroded by plasma than the grains of ceramic. Therefore, this increase ingrain size may cause the ceramic coating to be less prone to causeparticle contamination during subsequent processing. Accordingly, a heattreatment temperature and duration may be chosen based on a target grainsize for the ceramic coating.

For an alumina ceramic substrate and a ceramic coating of HPM or yttria,a heat treatment of 1500 C with a heat treatment duration of about 3-6hours may be performed. In one embodiment, the heat treatment durationis about 4 hours for a ceramic coating of yttria or the HPM ceramiccomposite.

In one embodiment, the ceramic article is maintained at a singletemperature for the duration of the heat treatment. Alternatively, theceramic article may be heated and/or cooled to multiple differenttemperatures within the temperature range during the heat treatment. Forexample, the ceramic article may be heat treated at a temperature of1500° C. for 4 hours, may then be heat treated to a temperature of 1700°C. for another 2 hours, and may then be heat treated at 1000° C. foranother three hours. Note that when multiple different heat treatmenttemperatures are used, the ceramic article may be heated and/or cooledat the ramping rate to transition between heat treatment temperatures.

At block 170, the ceramic article is cooled at the ramping rate. In oneembodiment, the ceramic article is cooled at the same ramping rate asthe ramping rate used to heat the ceramic article. In anotherembodiment, a different ramping rate is used to cool the ceramic articlethan was used to heat the ceramic article. The ceramic coating of theresultant heat treated ceramic article may have improved performancewith regards to particle contamination of processed substrates, plasmaerosion resistance, adhesion strength, porosity, amount and size ofcracks, and peeling resistance. Additionally, the resultant heat treatedceramic article may have a transition layer between the ceramic coatingand the ceramic substrate. Thus, ceramic lids, ceramic nozzles, processkit, and other ceramic internal process chamber components may be heattreated using process 150 to improve yield of manufactured products.Moreover, ceramic articles to which process 150 is applied may have areduced replacement frequency, and may reduce apparatus down time.

Note that process 150 may be performed as part of a manufacturingprocess for ceramic articles after a ceramic coating has been formed ona ceramic substrate. Additionally, process 150 may be periodicallyperformed on used ceramic articles to heal or repair those ceramicarticles. For example, a ceramic article may be heat treated usingprocess 150 before use, and may then be heat treated using process 150every few months, once a year, twice a year, or at some other frequency.The frequency with which to perform process 150 may depend on plasmaetch and/or plasma clean recipes that are used with the ceramic article.For example, if the ceramic article is frequently exposed toparticularly harsh plasma environments, then the ceramic article may beheat treated at an increased frequency.

Exposure to plasma may cause the ceramic coating to erode and/or corrodeover time. For example, the plasma may cause broken bonds to occur atthe surface of the ceramic coating, may generate ceramic particles thatcan contaminate processed substrates, may cause defects at the surfaceof the ceramic coating, may cause the ceramic coating to peel away fromthe ceramic substrate, and so on. Accordingly, as a ceramic articleages, the more particle contamination it is likely to cause. The heattreatment process 150 may be performed on such aged ceramic articles toreverse damage caused by the corrosive plasma environment. The heattreatment may heal defects and reduce particles for used ceramicarticles in addition to newly manufactured ceramic articles.Accordingly, process 150 may be performed on used ceramic articles toprolong their useful life.

Note that in addition to healing surface defects and minimizingparticles, the heat treatment process 150 may also be used to dry cleanceramic articles. Exposure to plasma environments may cause polymers toform on a surface of the ceramic article. These polymers may causeparticle contamination on substrates during subsequent processing.Often, a periodic wet clean procedure is performed to remove thepolymers from the ceramic article. In one embodiment, heat treatmentprocess 150 is performed instead of a wet clean process. The heattreatment process 150 may cause the polymers that coat the ceramicarticle to react with air or another gas in a high temperatureenvironment. This reaction may cause the polymer to become gaseous, andto leave the surface of the ceramic article. Therefore, the heattreatment process 150 can be used both to clean the ceramic article andto repair a surface of the ceramic article. Note that the temperatureand/or duration used for subsequent heat treatment processes may bedifferent from a temperature and/or duration used for an initial heattreatment process.

FIG. 2A shows micrographs 202-216 of a ceramic coating before theceramic coating is processed using a heat treatment, and after theceramic article has been processed using the heat treatment, inaccordance with embodiments of the present invention. The ceramiccoating shown in micrographs 202-216 is a HPM ceramic composite havingY₄Al₂O₉ and Y₂-xZr_(x)O₃.

Micrograph 202 shows a sample of the ceramic article prior to heattreatment. Micrograph 204 shows a zoomed in view of a region 208 shownin micrograph 202. Region 208 is relatively free from surface defects.Micrograph 204 illustrates a grain size of the ceramic coating.Micrograph 206 shows a zoomed in view of region 210 shown in micrograph202. Region 210 illustrates surface defects and surface particles of theceramic coating.

Micrograph 212 shows the sample of micrograph 202 after a heattreatment. As illustrated, an amount of surface defects has been reducedas a result of the heat treatment. Micrograph 214 shows a zoomed in viewof a region 218 shown in micrograph 212. Region 218 is relatively freefrom surface defects and surface particles. Micrograph 214 illustrates agrain size of the ceramic coating that is larger than the grain sizeshown in micrograph 204. Micrograph 216 shows a zoomed in view of region220 shown in micrograph 212. Region 220 illustrates surface defects ofthe ceramic coating. However, the surface defects shown in micrograph216 are less severe than the surface defects shown in micrograph 206,and surface particles have been substantially removed.

FIG. 2B shows additional micrographs 222-234 of a ceramic coating'ssurface at a 4,000-fold magnification before the ceramic coating isprocessed using a heat treatment, and after the ceramic coating has beenprocessed using heat treatments at various temperatures and treatmentdurations, in accordance with embodiments of the present invention.Micrograph 222 shows a sample of the ceramic coating prior to heattreatment. Micrograph 224 shows a sample of the ceramic coating after afour hour heat treatment at a temperature of 1300° C. Micrograph 226shows a sample of the ceramic coating after a four hour heat treatmentat 1400° C. Micrograph 228 shows a sample of the ceramic coating after afour hour heat treatment at 1500° C. Micrograph 234 shows a sample ofthe ceramic coating after a four hour heat treatment at a temperature of1600° C. As shown, increases in the temperature with a fixed heattreatment time cause a size and number of cracks to be reduced.Additionally, increases in the temperature cause a size and number ofpores to be reduced (thus reducing porosity).

Micrograph 230 shows a sample of the ceramic coating after a twenty fourhour heat treatment at a temperature of 1300° C. Micrograph 232 shows asample of the ceramic coating after a twenty four hour heat treatment ata temperature of 1400° C. As shown, heat treating the ceramic coatingover four hours did not significantly further reduce porosity or anamount of cracking. Accordingly, in one embodiment the heat treatmentduration is approximately four hours.

FIG. 2C shows additional micrographs 236-248 of a ceramic coating'ssurface at a 20,000-fold magnification before the ceramic coating isprocessed, and after the ceramic coating has been processed using heattreatments of various temperatures and treatment durations, inaccordance with embodiments of the present invention. Micrograph 236shows a ceramic coating before heat treatment. Micrograph 238 shows aceramic coating after a 4 hour heat treatment at 1300° C. Micrograph 240shows the ceramic coating after a 4 hour heat treatment at 1400° C.Micrograph 242 shows the ceramic coating after a 4 hour heat treatmentat 1500° C. Micrograph 248 shows the ceramic coating after a 4 hour heattreatment at 1600° C. The grain size shown in micrograph 248 is largerthan the grain size shown in micrograph 242, which is larger than thegrain size shown in micrograph 240, and so on. Thus, increases in heattreatment temperature cause an increase in grain size for the ceramiccoating.

Micrograph 244 shows a ceramic coating after a 24 hour heat treatment at1300° C. Micrograph 246 shows a ceramic coating after a 24 hour heattreatment at 1400° C. Thus, increases in heat treatment duration alsocause an increase in grain size for the ceramic coating. The ceramiccoating's grain size may initially be nano-sized prior to heattreatment, and may eventually grow larger than nano-sized due to theheat treatment. A temperature and/or duration for the heat treatment maybe selected based on target grain size. Increasing the treatmentduration may result in a non-uniform grain size, as shown in micrographs244 and 246.

FIG. 2D shows additional micrographs 250-256 of a ceramic coating'ssurface at a 10,000-fold magnification before the ceramic coating isprocessed, and after the ceramic coating has been processed, inaccordance with embodiments of the present invention. Micrographs 250and 254 show that prior to the heat treatment, the ceramic coatingincludes a high number of ceramic particles. Micrographs 252 and 256show that after the heat treatment, the ceramic particles are reduced oreliminated. In one embodiment, surface particle count may be reduced byas much as about 93%.

FIG. 3A illustrates micrographs 302-304 showing a cross sectional sideview of a ceramic article before and after heat treatment, in accordancewith one embodiment of the present invention. Micrograph 302 shows thatthe ceramic article includes a ceramic substrate 314 and a ceramiccoating 310 over the ceramic substrate 314. The illustrated ceramicsubstrate 314 is alumina and the illustrated ceramic coating 310 is theHPM ceramic composite.

Micrograph 304 shows the ceramic substrate 314 and ceramic coating 310along with a transition layer 312 that has been formed between theceramic coating 310 and the ceramic substrate 314. The illustratedtransition layer has a thickness of about 1-2 microns.

An elemental map 308 of the transition layer is also shown. Theelemental map 308 may provide an elemental analysis of the transitionlayer 312 based on energy dispersive X-ray spectroscopy (EDX). Theelemental map 308 shows that the transition layer 312 is composed ofcarbon, oxygen, aluminum and yttrium. The elemental map 308 furthershows that the atomic concentrations of the elements in the transitionlayer 312 are roughly 18% carbon, 46% oxygen, 23% aluminum and 13%yttrium. Thus, the transition layer 312 is shown to be Y₃Al₅O₁₂ (YAG).The transition layer may significantly improve the adhesion strength ofthe ceramic coating to the ceramic substrate.

FIG. 3B illustrates micrographs showing cross sectional side views of aceramic article at a 4,000-fold magnification before and after heattreatment at various temperatures and treatment durations, in accordancewith embodiments of the present invention. Micrograph 320 shows aninterface between a ceramic coating 310 and a ceramic substrate 314before heat treatment. Micrograph 322 shows an interface between theceramic coating 310 and the ceramic substrate 314 after a 4 hour heattreatment at 1300° C. Micrograph 324 shows an interface between theceramic coating 310 and the ceramic substrate 314 after a 4 hour heattreatment at 1400° C. Micrograph 326 shows an interface between theceramic coating 310 and the ceramic substrate 314 after a 4 hour heattreatment at 1500° C. Micrograph 332 shows an interface between theceramic coating 310 and the ceramic substrate 314 after a 4 hour heattreatment at 1600° C. Micrograph 328 shows an interface between theceramic coating 310 and the ceramic substrate 314 after a 24 hour heattreatment at 1300° C. Micrograph 330 shows an interface between theceramic coating 310 and the ceramic substrate 314 after a 24 hour heattreatment at 1300° C.

As shown in micrographs 326, 330 and 332, a transition layer 312 formsbetween the ceramic coating 310 and the ceramic substrate 314 during theheat treatment under certain conditions. At a heat treatment temperatureof 1300° C., no transition layer may be formed, regardless of the heattreatment duration. At a heat treatment temperature of 1400° C., notransition layer may be detectable after 4 hours of processing, but atransition layer 312 may be detectable after 24 hours of processing. Atheat treatment temperatures of 1500° C. and 1600° C., transition layer312 may be detectable after 4 hours of processing.

A thicker transition layer is shown to be formed for increased treatmenttemperatures and for increased treatment durations. Temperature may havea greater impact on transition layer thickness than duration. As shown,a heat treatment with a duration of 4 hours and a temperature of 1500°C. may produce a transition layer 312 having a thickness that isslightly thicker than a transition layer 312 produced by a heattreatment with a duration of 24 hours and a temperature of 1400° C.

FIG. 3C illustrates micrographs 350-356 showing cross sectional sideviews of a ceramic article at a 20,000-fold magnification before andafter heat treatment, in accordance with embodiments of the presentinvention. Micrographs 350 and 354 show an interface between the ceramiccoating 310 and the ceramic substrate 314 prior to heat treatment. Gaps370 are shown between the ceramic substrate 314 and the ceramic coating310 prior to the heat treatment. These gaps may contribute to futuredelamination of the ceramic coating 310 from the ceramic substrate 314.Micrographs 352 and 356 show that a transition layer 312 forms at theinterface between the ceramic coating 310 and the ceramic substrate 314during heat treatment. Additionally, micrographs 352 and 356 show thatthe gaps 370 present prior to heat treatment are eliminated or reducedas a result of heat treatment. This may reduce a likelihood ofdelamination, and may improve an adhesion or bond strength of theceramic coating 310 to the ceramic substrate 314.

FIG. 3D illustrates a phase composition comparison of an HPM ceramiccomposite coating before and after heat treatment, in accordance withone embodiment of the present invention. As shown, the thermal treatmentdid not significantly change a phase composition of the ceramic coatingor the ceramic substrate.

Surface morphology of the ceramic coating may be represented usingsurface roughness parameters and/or surface uniformity parameters. Thesurface morphology may also be represented using porosity, crackingand/or void parameters. Measured parameters that represent porosity mayinclude a pore count and/or an average pore size. Similarly, measuredparameters that represent voids and/or cracking may include an averagevoid/crack size and/or a void/crack count.

Measured parameters that represent particle count are a tape peel testparticle count and a liquid particle count (LPC). The tape test may beperformed by attaching an adhesive tape to the ceramic coating, peelingthe tape off, and counting a number of particles that adhere to thetape. The LPC may be determined by placing the ceramic article in awater bath (e.g., a de-ionized (DI) water bath) and sonicating the waterbath. A number of particles that come off in the solution may then becounted using, for example, a laser counter.

Adhesion strength may be determined by applying a force (e.g., measuredin mega pascals) to the ceramic coating until the ceramic coating peelsoff from the ceramic substrate. In one embodiment, the adhesion strengthfor the ceramic coating is on the order of 4 Mega pascals (MPa) beforethe heat treatment and on the order of 12 MPa after the heat treatment.Thus, the adhesion strength of the ceramic coating to the ceramicsubstrate after the heat treatment may be about three times strongerthan the adhesion strength prior to the heat treatment.

Adhesion strength, porosity, cracking and particle count values for theceramic coating may improve as a result of the heat treatment.Additionally, grain size may increase and hardness may decrease as aresult of the heat treatment. Empirical evidence also shows that theamount of particle contamination caused during plasma etch processes byceramic coated lids and ceramic coated nozzles is decreased as a resultof the heat treatment. Empirical evidence also shows that peeling of theceramic coating from the ceramic substrate is reduced as a result of theheat treatment. Additionally, surface roughness of the ceramic coatingis reduced as a result of the heat treatment.

Note that for heat treatments of up to about 1200° C., the interactionbetween particles and a surface of the ceramic coating may be dominatedby a van der Waals force, according to the following equation:

$\begin{matrix}{F = \frac{A}{12\pi \; H^{2}}} & \left( {{equation}\mspace{14mu} 1} \right)\end{matrix}$

where F is force, A is area and H is distance. As the heat treatmenttemperature increases from room temperature to about 500° C., the vander Waals force may weaken, and thermal expansion may induce an increasein the distance H. As the heat treatment temperature increases from 500°C. to about 1200° C., the van der Waals force may strengthen due atleast in part to decreases in the distance H. Such reductions indistance may be due to the substrate surface absorbing particles and/ordeformations.

At temperatures between about 1200° C. and 1800° C., a liquid film maybe formed between particles and the ceramic coating surface. Betweenabout 1200° C. and 1500° C., the liquid film may be a thin liquid film,and between about 1500° C. and 1800° C., the liquid film may be a thickliquid film. At temperatures up to about 1800° C., the interactionbetween the particles and the ceramic coating's surface may be dominatedby interaction through the liquid by a capillary force, according to thefollowing equation:

F=4πγR cos θ  (equation 2)

where F is force, γ is liquid-air surface tension, R is effective radiusof the interface between the particles and substrate surface, and θ iscontact angle. At these temperatures, particles may be diffused into theliquid, and may be re-grown on a corresponding grain. This may causeparticles to be removed from the substrate surface, even after theceramic article has cooled.

For the HPM ceramic composite and yttria, 1800° C. is the sinteringtemperature. Accordingly, at temperatures at or above around 1800° C., aliquid phase is formed in the ceramic coating between powders. Thesepowders may melt into liquid and grow into grains of increasing size.Atoms may be diffused from high energy grains to low energy grains untilan equilibrium is reached. Accordingly, in one embodiment, the heattreatment is performed at temperatures below about 1800° C.

The preceding description sets forth numerous specific details such asexamples of specific systems, components, methods, and so forth, inorder to provide a good understanding of several embodiments of thepresent invention. It will be apparent to one skilled in the art,however, that at least some embodiments of the present invention may bepracticed without these specific details. In other instances, well-knowncomponents or methods are not described in detail or are presented insimple block diagram format in order to avoid unnecessarily obscuringthe present invention. Thus, the specific details set forth are merelyexemplary. Particular implementations may vary from these exemplarydetails and still be contemplated to be within the scope of the presentinvention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.In addition, the term “or” is intended to mean an inclusive “or” ratherthan an exclusive “or.”

Although the operations of the methods herein are shown and described ina particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A ceramic article comprising a ceramic substrateand a ceramic coating on the ceramic substrate, the ceramic articlehaving been prepared by a process comprising: performing a thermalspraying process to form the ceramic coating on the ceramic substrate,the ceramic coating having an initial porosity and an initial amount ofcracking; heating the ceramic article to a temperature range betweenabout 1000° C. and about 1800° C.; performing heat treatment of theceramic article at one or more temperatures within the temperature rangefor a duration to reduce a porosity of the ceramic coating to below theinitial porosity and to reduce an amount of cracking of the ceramiccoating to below the initial amount of cracking, wherein the ceramicarticle is heat treated at below a sintering temperature for the ceramiccoating to prevent sintering of the ceramic coating; and cooling theceramic article after the heat treatment, wherein after the heattreatment the ceramic coating is not sintered, has a reduced amount ofcracking that is below the initial amount of cracking, and has a reducedporosity that is below the initial porosity.
 2. The ceramic article ofclaim 1, wherein the ceramic coating additionally has an initialparticle count and an initial adhesion strength, and wherein after theheat treatment the ceramic coating has a reduced particle count and anincreased adhesion strength of about 12 Mega Pascals.
 3. The ceramicarticle of claim 1, wherein the ceramic substrate and the ceramiccoating each consists essentially of at least one of Y₂O₃, Al₂O₃,Y₄Al₂O₉, Y₃Al₅O₁₂ (YAG), Quartz, SiC, Si₃N₄, AlN or SiC—Si₃N₄, andwherein the ceramic substrate has a different composition than theceramic coating.
 4. The ceramic article of claim 1, wherein the heattreatment causes the ceramic coating to react with the ceramic substrateto form a transition layer between the ceramic substrate and the ceramiccoating, and wherein the duration and the temperature range are selectedto cause the transition layer to have a thickness of about 1 microns toabout 5 microns.
 5. The ceramic article of claim 4, wherein: the ceramicsubstrate comprises Al₂O₃; the ceramic coating comprises Y₄Al₂O₉ and asolid solution of Y₂O₃—ZrO₂; and the transition layer comprisesY₃Al₅O₁₂.
 6. The ceramic article of claim 1, wherein the ceramic articleis a refurbished ceramic article that has been used in a plasma etchprocess, and wherein the heating, the performing of the heat treatmentand the cooling have been performed after the plasma etch process toreduce an increased surface defect density caused by the plasma etchprocess.
 7. The ceramic article of claim 6, wherein the plasma etchprocess causes polymers to form on the ceramic article, whereinperforming the heat treatment in the presence of oxygen dry cleans theceramic article by causing the polymers to react with the oxygen tobecome gases, and wherein the refurbished ceramic article issubstantially free of the polymers.
 8. The ceramic article of claim 1,wherein: the heating is performed at a ramping rate of about 0.1° C. perminute to about 20° C. per minute; the duration of the heat treatment isof up to about 24 hours; and the heating is performed at a rate of about0.1-20° C. per minute.
 9. The ceramic article of claim 1, wherein theheat treatment causes a grain size of the ceramic coating to increase,and wherein the duration and the temperature range are selected so thatthe ceramic coating has a target grain size.
 10. A method comprising:performing a thermal spraying process to form a ceramic coatingcomprising at least one of a yttrium-based oxide or an erbium-basedoxide on a ceramic article, wherein the ceramic coating has an initialporosity and an initial amount of cracking; heating the ceramic coatingto a temperature range between about 1000° C. and about 1800° C.; heattreating the ceramic coating at one or more temperatures within thetemperature range for a duration to reduce a porosity and an amount ofcracking of the ceramic coating, wherein the ceramic coating is heattreated at below a sintering temperature for the ceramic coating toprevent sintering of the ceramic coating, and wherein the heat treatingcauses the ceramic coating to react with the ceramic article to form atransition layer between the ceramic article and the ceramic coating;and cooling the ceramic coating after the heat treating, wherein afterthe heat treating the ceramic coating is not sintered, has a reducedamount of cracking that is below the initial amount of cracking, and hasa reduced porosity that is below the initial porosity.
 11. The method ofclaim 10, wherein the ceramic article comprises Al₂O₃, the ceramiccoating comprises Y₄Al₂O₉ and a solid solution of Y₂O₃—ZrO₂, and thetransition layer comprises Y₃Al₅O₁₂.
 12. The method of claim 10,wherein: the heating is performed at a ramping rate of about 0.1-20° C.per minute; the duration of the heat treating is up to about 24 hours;and the cooling is performed at a rate of about 0.1-20° C. per minute.13. The method of claim 10, wherein the ceramic coating additionally hasan initial particle count and an initial adhesion strength, and whereinafter the heat treating the ceramic coating has a reduced particle countand an increased adhesion strength.
 14. The method of claim 10, whereinthe heat treating is performed for a specified duration, and wherein thespecified duration and the temperature range are selected to cause thetransition layer to have a thickness of about 1 microns to about 2microns.
 15. The method of claim 10, further comprising: after theceramic article has been used in a plasma etch process, repeating theheating, the heat treating and the cooling to reduce an increasedsurface defect density caused by the plasma etch process.
 16. The methodof claim 15, wherein the plasma etch process causes polymers to form onthe ceramic article, and wherein repeating the heat treating in thepresence of oxygen dry cleans the ceramic article by causing saidpolymers to react with the oxygen to become gases.
 17. The method ofclaim 10, wherein the heat treating causes a grain size of the ceramiccoating to increase, and wherein a duration of the heat treating and thetemperature range are selected so that a target grain size is reached.18. The method of claim 10, wherein the ceramic coating comprises asolid solution comprising Y₂O₃ and at least one of ZrO₂, Al₂O₃, SiO₂,B₂O₃, Er₂O₃, Nd₂O₃, Nb₂O₅, CeO₂, Sm₂O₃ or Yb₂O₃.
 19. The method of claim10, wherein: the heat treating is performed using at least one of lasersurface treatment, electron beam surface treatment, flame surfacetreatment, or plasma treatment; and the thermal spraying process is aplasma spraying process.
 20. A method comprising: receiving a heattreated ceramic article comprising a ceramic substrate and a ceramiccoating that has been used in a plasma etch process, wherein the ceramiccoating has an initial surface defect density caused by the plasma etchprocess; heating the ceramic article to a temperature range betweenabout 1000° C. and about 1800° C. at a ramping rate of about 0.1° C. perminute to about 20° C. per minute; heat treating the ceramic article atone or more temperatures within the temperature range for a duration ofup to about 24 hours to reduce the surface defect density caused by theplasma etch process; and cooling the ceramic article at the ramping rateafter the heat treating, wherein after completing the heat treating theheat treated ceramic article has a new surface defect density levelbelow the surface defect density level caused by the plasma etchprocess.